Contractile unit having a position sensor means

ABSTRACT

A contractile unit comprising a contractile hose extending between two spaced head pieces and adapted to perform a longitudinal contraction on being subjected to internal pressure, and a position sensor means responsive to the distance between the head pieces. The position sensor means possesses a microwave generator arranged on one of the head pieces and adapted to emit microwaves into the interior space of the contractile unit, an evaluating means being provided responsive to the distance between the head pieces using transit time measurement, phase comparison of the emitted and reflected wave or using determination of the resonant frequency.

This application is a National Phase application of InternationalApplication No. PCT/EP03/04859 filed May 9, 2003, which claims prioritybased on German patent application No. 102 25 246.7 filed on Jun. 7,2002, which are incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to a contractile unit comprising a contractilehose extending between two spaced apart head pieces and adapted toperform a longitudinal contraction.

BACKGROUND OF THE INVENTION

Such contractile units are for example disclosed in the assignee'sbrochure “Fluidic Muscle”, the European patent publication 0 161 750 B1,the German patent publication (utility model) 29,906,626, the Germanpatent publication (utility model) 29,908,008 or the German patentpublication (utility model) 20,112,633 and are suitable for highly exactpositioning while having a simple and low-wear structure involvingrelatively low costs. Extremely high setting forces may be produced.

For precise positioning position sensors or angle sensors are requiredin principle for all servo systems. In conjunction with servo cylindersa plurality of such position sensors and sensor means is available whichare based on the most various different principles of measurement. Inthe case of contractile units of the above noted type the same arehowever for the most part unsuitable or badly suited.

SUMMARY OF THE INVENTION

One object of the present invention is accordingly to create a positionsensor means which is highly suitable for such contractile units and isable to be produced simply and at a low cost while ensuring highaccuracy.

This aim is to be attained by a contractile unit with a position sensormeans, which comprises the features of claim 1.

The advantages of the design in accordance with the invention are moreparticularly that such a microwave generator, which is alreadycommercially available at an extremely low price in a miniaturized form,may be very easily mounted on the inner side of one of the head piecesor may be integrated in one of the head pieces. Owing to the arrangementin the interior space of the contractile unit without external measuringelements the compactness of the contractile unit is not reduced andmechanical damage or interference is excluded as regards the positionsensor means to a substantial extent. One of the principal advantages ofsuch contractile units, namely the complete sealing and accordingly thesmall amount of working fluid needed, is not impaired by the positionsensor means. The measurement of the distance between the head piecesand accordingly the detected position may be performed with greataccuracy.

Further advantageous developments of the contractile unit as defined inclaim 1 are indicated in the dependent claims.

The microwave generator is advantageously also designed as a microwavereceiver so that the reflected microwaves may be detected using the samecompact component. This results in a simplification of the electricalconnections of the position sensor means.

In accordance with an advantageous design the evaluating means comprisesmeans for phase comparison of the emitted microwave signal and of themicrowave signal reflected at the oppositely placed metallic head pieceand furthermore for determination of the phase difference as a measureof the distance. The accuracy of measurement is accordingly in the rangeof half a wavelength.

In accordance with a further advantageous design of the invention theevaluating means possesses a frequency generator for variably settingthe microwave frequency, a resonance detector being provided for theresonant frequency. For this purpose the frequency generator ispreferably designed in the form of a ramp generator operating in such amanner that on detection of the resonant frequency by the resonancedetector and frequency involved is then stored or held as themeasurement of the distance. To simplify evaluation a frequency reduceris provided for the resonant frequency in the evaluation means.

The contractile hose is preferably provided with electrically conductiveparticles or strand elements such as wires, are provided so that theentire contractile unit contributes to influencing the resonantfrequency and the entire contractile unit may serve as a microwave waveguide.

According to a convenient design, the microwave generator is designed asa coupled probe transmitting and receiving microwaves. As an alternativeto this, the microwave generator may also be designed as a cavityresonator with a resonance space open toward the oppositely placed headpiece of the contractile unit. This provides a satisfactory focussing ordirectionality of the emitted microwave beam.

BRIEF DESCRIPTION OF THE DRAWINGS

One working example of the invention is represented in the drawing anddescribed in ²detail in the following account. The single FIGURE shows acontractile unit or element unit in longitudinal section, one of thehead pieces being provided with a cavity resonator as a position sensormeans.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The contractile element is only diagrammatically represented in thesingle figure for simplification. A more detailed representation is tobe found for example in the initially mentioned German patentpublication (utility model) 29,906,626. A contractile hose 10 of anelastic rubber or plastic material is sealed off both ends by headpieces 11 and 12. In the wall of the contractile hose 10, there is aconventional flexible strand structure which is not illustrated tosimplify the drawing and which in the present case may consist ofmetallic strand structures 22 in order to let the contractile unitfunction as a microwave wave guide. The wall can also comprise othermetallic conductive particles 24. The connection of the contractile hose10 with the two head pieces 11 and 12 is such that the contractile hose10 provided with the strand structure 22 is able to transmit tensionforces to the respective head piece 11 and 12. The attachment may forexample be as part of a clamping connection as is described by way ofexample in the said European patent publication 0 161 750 B1. Otherattachment means are also possible.

Into the interior space 13 delimited by the contractile hose 10 and thetwo head pieces 11 and 12 there opens a fluid duct 14, that extendsthrough one of the head pieces 11 and whose outer end is provided with aconnection means 15, by way of which a fluid line, extending from apressure source, may be connected. In principle several fluid ductscould be provided as well. In connection with a control valvearrangement, not illustrated, there is accordingly the possibility ofsupplying and removing a fluid pressure medium through the fluid duct 14into the interior space 13 and from such space.

The figure shows the contractile hose 10 in the activated state, that isto say with the interior space 13 subject to pressure. In this state thecontractile hose 10 is radially expanded and simultaneously axiallycontracted so that the two head pieces 11 and 12 are moved togetheraxially. In the deactivated state, that is to say with the interiorspace free of pressure, the contractile hose 10 assumes an essentiallytubular configuration and the two head pieces 11 and 13 moved away fromthe one another. It is in this manner that by matched fluid action inthe interior space 13 an axial stroke of the head pieces 11 and 12 inrelation to one another may be produced.

As a position sensor means for detecting the relative position of thetwo head pieces 11 and 12, the one head piece 11 is provided at a sidefacing the interior space with a microwave cavity resonator 16. Same maybe attached to the head piece 11 or integrated in it. The cavityresonator 16 possesses a resonance space that is open toward theopposite head piece 12, by means of which microwaves may be emittedtoward the opposite head piece 12. There they are reflected and passback to the cavity resonator 16, which is provided with a suitabledetecting means, not illustrated. Such a cavity resonator for measuringthe distance is described in the German patent publication 19,807593 A1so that a detailed representation is not required.

The cavity resonator 16 is driven by a ramp frequency generator 17 sothat the frequency is preset. The receiving part of the cavity resonator16 is connected with a resonance detector 18, which for examplecomprises a two-stage differentiator and a comparator, and constantlymonitors the received signal for resonance. The resonance expressesitself as a steep slope of the receive signal. As soon as an evaluatingmeans 19, connected with the ramp frequency generator 17 and theresonance detector 18, detects resonance, the ramp-like frequencyincrease is halted and the frequency held. It is reduced usinga-frequency divider 20 and communicated to the evaluating means 19 toserve as a measure for the distance apart of the two head pieces 11 and12.

The resonant frequency is dependent on the distance apart of the twohead pieces 11 and 12 and may be also influenced by the conductive wallof the contractile hose 10. For each condition of the contractileelement there is a particular resonant frequency so that merely thetransmission frequency must be varied in each case until the resonantfrequency and the transmission frequency are the same. The receivingmeans, for example in the form of a detector diode 26, of the cavityresonator 16 recognizes a power drop on the resonant frequency beingreached.

A value converted from the respective resonant frequency to representthe distance apart can be indicated on a display 21 and/or evaluated insome other manner.

The frequency generator 17, the resonance detector 18 and the frequencydivider 20 may naturally be components of the evaluating means 19instead of being separate units. Moreover, other evaluating means inaccordance with the state of the art are possible.

As an alternative to the cavity resonator 16 the microwave generatorarranged on the head piece 11 may also for example be in the form of acoupled probe 28, as is described in more detail in the German patentpublication 19,833,220 A1 for measuring the distance. The microwavesignal is supplied by way of a coupled probe into the interior space ofthe contractile element 10, the operation being so performed that in afirst step the absolute distance between the entry point on the lefthead piece 11 and the right head piece 12 is measured, for example bytransit time measurement for the frequency modulated transmitted signal.Then a standing wave is produced in the interior space, whose shift isperformed by the axial change in length of the two head pieces towardeach other. By phase evaluation of the signal, which as regardsfrequency is reduced in a manner like in the previous example of theinvention, the changing distance between the head pieces is measured. Inthe German patent publication 19,833,330 A1 various working examples aredescribed, which may be employed as alternatives.

1. A contractile unit comprising a contractile hose extending betweentwo spaced head pieces and adapted to perform a longitudinal contractionon being subjected to internal pressure, and a position sensor meansresponsive to the distance between the head pieces, which possesses amicrowave generator arranged on one of the head pieces and adapted toemit microwaves into the interior space of the contractile unit, anevaluating means being provided responsive to the distance between thehead pieces, by transit time measurement, by phase comparison of theemitted and reflected wave or by determination of the resonantfrequency, the contractile hose comprising at least one of electricallyconductive particles, electrically conductive strand elements, andwires.
 2. The contractile unit as set forth in claim 1, wherein themicrowave generator is also adapted to function as a microwave receiver.3. The contractile unit as set forth in claim 1, wherein the evaluatingmeans comprises means for phase comparison of the emitted microwavesignal and the reflected microwave signal and for phase differencedetermination as a measure of the distance.
 4. The contractile unit asset forth in claim 1, wherein the evaluating means is provided with afrequency generator for variably setting the microwave frequency and inthat a resonance detector is provided responsive to the resonantfrequency.
 5. The contractile unit as set forth in claim 4, wherein thefrequency generator is provided in the form of a ramp frequencygenerator and on detection of the resonant frequency by the resonancedetector the present frequency is held as a measure for the distance. 6.The contractile unit as set forth in claim 5, wherein a frequencyreducer is provided for the evaluation of the resonant frequency in theevaluating means.
 7. The contractile unit as set forth in claim 1,wherein the microwave generator is designed in the form of at least oneof a coupled probe and a detector diode transmitting and receivingmicrowaves.
 8. The contractile unit as set forth in claim 1, wherein themicrowave generator is designed in the form of a cavity resonator with aresonance space open toward the opposite head piece.
 9. The contractileunit as set forth in claim 2, wherein the evaluating means comprisesmeans for phase comparison of the emitted microwave signal and thereflected microwave signal and for phase difference determination as ameasure of the distance.
 10. The contractile unit as set forth in claim2, wherein the evaluating means is provided with a frequency generatorfor variably setting the microwave frequency and in that a resonancedetector is provided responsive to the resonant frequency.